One type of offshore oil and gas well utilizes a subsea Christmas or production tree. The tree lands on top of a high pressure wellhead housing, which is in turn supported by a low pressure wellhead housing. The high pressure wellhead housing contains one or more strings of casing.
In one type of subsea tree, known as a horizontal tree or a spool tree, the tree is landed on the high pressure wellhead housing before the tubing hanger and tubing are run. After the tree is landed, the tubing is lowered through the tree and the tubing hanger lands in the tree. The tree has a lateral production outlet, and the tubing hanger has a lateral production passage that must align with the production outlet when it lands. In a producing well, well fluid flows up the tubing and out the production outlet of the tree.
The tree and the tubing hanger may have additional ports that must register with each other, such as ports for hydraulic fluid for a downhole safety valve. One type of orientation system for orienting the tubing hanger comprises a sleeve secured to the lower end of the tree while the tree is being run. The sleeve stabs sealingly into the uppermost casing hanger in the high pressure wellhead housing. The sleeve has an internal helical profile or “muleshoe” formed in it. The tubing hanger has an orientation pin that engages the helical edge to rotate the tubing hanger as it is landed in the tree.
While these systems work well, the orientation sleeve guide edge as described presents an obstacle for components attached to the tubing, such as an electrical submersible pump. The pump is normally larger in diameter than the tubing and typically has a power cable extending upward alongside the tubing. The power cable might catch and be damaged on the orientation sleeve guide edge.
Additionally, an orientation system as described requires installing all of the casing hangers before running the tree. In some cases, the operator desires to land the tree on the high pressure wellhead housing before the last casing string has been run. The tree would not have an orientation sleeve on its lower end that stabs into a casing hanger because the last casing hanger would not yet have been run. In a drill-through system, after landing the tree, the operator lowers the drill pipe through the tree to drill the well to final depth, and then installs the final casing hanger and casing through the tree. Subsequently, the operator will run the tubing hanger, and other provisions have to be made to orient the tubing hanger because the tree would not have an orientation sleeve as described.
A drill-through horizontal tree may have an orientation sleeve secured to it before running the tree, but if so, the result may be a smaller inner diameter of the through-bore than desired. The sleeve would need to be protected from damage due to the drill string passing through the sleeve during drilling. An orientation sleeve can be installed in the tree or wellhead housing after the drilling has been completed and the casing hanger run, but this procedure necessitates an additional trip from the surface to the subsea wellhead assembly. The additional trip is costly because of the large expense of operating an offshore drilling rig.
Retractable guide pins have been used for orienting tubing hangers in subsea wellhead systems other than horizontal trees. FIG. 6 of U.S. Pat. No. 7,063,157 discloses a helix 104 on a tubing hanger running tool 96 that engages a retractable pin 88 in tubing hanger orientation body 74. Tubing hanger 48 (FIG. 2) lands in wellhead housing 20, not in a horizontal tree. U.S. Pat. No. 4,721,163 shows a retractable pin 21 in a orientation spool 26 that engages a guide slot 66 on a tubing hanger running tool 59.